This invention relates generally to electronically controlled fuel injection systems and, more particularly, to a method and apparatus for adjusting the duration of each fuel shot associated with a multi-shot fuel injection to compensate for the inherent delay between electrical activation of the fuel injector and the actual start of fuel injection.
Electronically controlled fuel injectors are well known in the art including hydraulically actuated electronically controlled fuel injectors, mechanically actuated electronically controlled fuel injectors, and digitally controlled fuel valves. Electronically controlled fuel injectors typically inject fuel into a specific engine cylinder as a function of an injection signal received from an electronic controller. These signals include waveforms that are indicative of the desired timing and quantity of fuel to be injected into the cylinders. As used throughout this disclosure, an injection event is defined as the injections that occur in a cylinder during one cycle of the engine. For example, one cycle of a four cycle engine for a particular cylinder, includes an intake, compression, expansion, and exhaust stroke. Therefore, the injection event in a four stroke engine includes the number of injections, or shots, that occur in a cylinder during the four strokes of the piston. The term shot as used in the art may also refer to the actual fuel injection or to the command current signal to a fuel injector or other fuel actuation device indicative of an injection or delivery of fuel to the engine. Each injection waveform may include a plurality of distinct and/or rate shaped fuel shots delivered to a cylinder during a particular fuel injection event.
Techniques utilizing multiple fuel injection techniques have been utilized to modify the burn characteristics of the combustion process in an attempt to reduce emission and noise levels. Multiple fuel injection involves splitting the total fuel delivery to the cylinder during a particular injection event into a number of separate fuel injection shots, such as into two fuel shots generally referred to as a main injection, and an anchor injection.
Due to the construction and operation of both mechanically actuated electronically controlled fuel injectors as well as hydraulically actuated electronically controlled fuel injectors, there is a delay or dead band associated with the injection current duration and the actual start of fuel injection for a multi-shot fuel injection event. This delay is known in the art as the SOC/SOI delay, that is, the delay from the start of current (SOC) to the start of the injection (SOI).
If only one shot is used, the SOC/SOI delay may be accounted for by the governor as a fuel offset. But as multiple shots come and go during engine operation, the governor must likewise adjust with additional offsets for each pulse. Furthermore, if mechanically actuated injections have different pressure capabilities for each shot due to cam profile, then different physical quantities of fuel will be delivered for each shot with the same electronic duration. Therefore, delays arise during multiple injection events that may not be experienced during single injection events. The delays create issues with the overall injection strategy with respect to injection timing, duration, and fuel quantity that do not occur with single injection strategies.
Because the current duration associated with each separate fuel shot in a particular fuel injection event is determined based upon the amount of fuel desired to be apportioned to that particular fuel shot, any delay in activation of the fuel injector or other fuel injecting device to start fuel injection, if not accounted for, may result in delivering a less than desired amount of fuel during that particular fuel shot. For example, inaccuracies in one fuel shot may effect the fuel injected into subsequent shots, and the fuel injection profile, and therefore lead to reduced efficiency and increased emissions for a particular injection event. The effects of this delay are sometimes more prominent in mechanically actuated fuel injectors due to the different velocity and acceleration profiles and operation of the various cams or other mechanical configurations associated therewith for actuating such injectors as compared to hydraulically actuated fuel injectors. Nevertheless, the SOC/SOI delay does affect fuel delivery and efficiency in both types of electronically-controlled fuel injectors.
It is, therefore, desirable to improve the performance of electronically controlled fuel injectors and to adjust the current duration of each fuel shot associated with a particular multi-shot fuel injection event in order to compensate for the SOC/SOI delay and to deliver the appropriate and desired amount of fuel during each such fuel shot.
Accordingly, the present invention is directed to overcoming one or more of the problems as set forth above.
In one aspect of the present invention there is disclosed an a method for controlling the injection current duration of a fuel injector to inject a predetermined volume of fuel during each fuel shot of a multiple shot event. The comprises the steps of sensing engine speed, determining an initial injection current duration for each fuel shot, establishing an injection delay for each fuel shot, and determining a corrected injection current duration to inject the predetermined volume of fuel for each shot based upon the initial injection current duration, the injection delay and the engine speed.